Hi,
 
I have mixed thoughts on this ... but in the end, it would depend on how clean the air is and runs through the room. I would recommend having an ionizer to ensure the air is clean, so the computer and the instruments do not gain dust that is harmful to it.
 
I have those little fans that grab the air in the room and re-circulate it, with one problem ... I have to take the computer outside every two months and use the bottled air to clean them!
 
Fireplace? ... I doubt it would be any better!